Cisco credits Pratap Ramamurthy and Shai Rubin of the Wisconsin Safety Analyzer group (WiSA) in the Computer Science department at the University of Wisconsin with reporting the fragmented packet IPS evasion vulnerability.

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Cisco Security Advisory: Cisco Intrusion Prevention System Management
Interface Denial of Service and Fragmented Packet Evasion Vulnerabilities
Document ID: 71558
Advisory ID: cisco-sa-20060920-ips
http://www.cisco.com/warp/public/707/cisco-sa-20060920-ips.shtml
Revision 1.0
For Public Release 2006 September 20 1600 UTC (GMT)
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Contents
========
Summary
Affected Products
Details
Impact
Software Version and Fixes
Workarounds
Obtaining Fixed Software
Exploitation and Public Announcements
Status of this Notice: FINAL
Distribution
Revision History
Cisco Security Procedures
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Summary
=======
Cisco Intrusion Prevention System (IPS) software contains a denial of
service vulnerability in web administration interface involving
malformed Secure Socket Layer (SSL) packets and a fragmented packet
evasion vulnerability.
There is a workaround for the web administration interface SSL denial
of service vulnerability. There is no workaround for the fragmented
packet IPS evasion vulnerability.
Cisco has made free software available to address these vulnerabilities
for affected customers.
This advisory is posted at
http://www.cisco.com/warp/public/707/cisco-sa-20060920-ips.shtml.
Affected Products
=================
Vulnerable Products
+------------------
The following Cisco IPS/IDS versions are vulnerable to the web
administration interface SSL denial of service issue:
* Cisco IDS 4.1(x) software prior to 4.1(5c)
* Cisco IPS 5.0(x) software prior to 5.0(6p1)
* Cisco IPS 5.1(x) software prior to 5.1(2)
The following Cisco IPS versions are vulnerable to the fragmented
packet IPS evasion issue:
* Cisco IPS 5.0(x) software prior to 5.0(6p2)
* Cisco IPS 5.1(x) software prior to 5.1(2)
All platforms running vulnerable versions of Cisco IPS/IDS software are
affected. This includes 4200 series appliances, IDSM2, NM-CIDS router
modules, and ASA IPS modules (also referred to as Advanced Inspection
and Prevention (AIP) Security Services Module [SSM]).
To determine the version of software running on an IPS/IDS device, log
in to the IPS/IDS device via SSH or the console and issue the command
show version.
sensor#show version
Application Partition: Cisco Intrusion
Prevention System, Version 5.1(2)S242.0
Products Confirmed Not Vulnerable
+--------------------------------
No other Cisco products are currently known to be affected by these
vulnerabilities.
Cisco IOS software images including the IPS feature set are not
vulnerable to the IPS evasion vulnerability if Virtual Fragment
Reassembly (VFR) is enabled. If VFR is not enabled, fragmented IP
traffic is not inspected by the IPS component which may allow malicious
traffic to evade detection. Please consult the IOS IPS documentation
for more information.
http://www.cisco.com/en/US/products/ps6634/products_white_paper0900aecd8043bc32.shtml
Details
=======
Cisco Intrusion Prevention and Detection Systems are a family of
network security devices that provide network-based threat prevention
services.
The web administration interface of Cisco IPS/IDS devices contains a
denial of service vulnerability. It is possible to send a malformed
SSLv2 Client Hello packet to the IPS/IDS web administration interface,
which may cause the process (mainApp) responsible for managing remote
access to fail. This results in an IPS/IDS device becoming unresponsive
to all future remote management requests through the web administration
interface or the command-line interface (CLI) via SSH and the console.
This vulnerability is documented in Cisco bug IDs CSCsd91720 and
CSCsd92033. This vulnerability was originally fixed in Cisco IPS
version 5.1(2).
By using a specially crafted sequence of fragmented IP packets, it is
possible for malicious traffic to evade inspection by a Cisco IPS
device. This may allow an attacker to circumvent the protection
provided by an IPS device and access internal systems. IPS devices
running in inline and promiscuous modes are affected. This
vulnerability is documented in Cisco bug IDs CSCse17206 and CSCsf12379.
This vulnerability was originally fixed in Cisco IPS version 5.1(2).
Impact
======
Successful exploitation of the web administration interface SSL denial
of service vulnerability may result in the failure of the mainApp
process. If the mainApp process fails, the following tasks will cease
operation:
* Reporting alerts to remote monitoring systems
* Automated modification of access control lists (ACLs) on remote
firewall systems (PIX and IOS)
* Sending SNMP traps
Even though the mainApp has failed, the IPS/IDS device will continue to
perform inspection of traffic for malicious activity. If configured,
the device will continue to drop packets/connections inline and send
TCP resets in response to any malicious activity. IPS/IDS devices must
be rebooted to recover from this vulnerability. If an IPS/IDS device is
configured with a service account, it is possible to log in to an
affected device with the service account via SSH or the console and
manually reboot the device.
Successful exploitation of the fragmented packet IPS evasion
vulnerability may result in an attacker being able to evade detection
by an IPS device. This could allow protected systems to be covertly
attacked.
Software Version and Fixes
==========================
When considering software upgrades, also consult
http://www.cisco.com/go/psirt and any subsequent advisories to
determine exposure and a complete upgrade solution.
In all cases, customers should exercise caution to be certain the
devices to be upgraded contain sufficient memory and that current
hardware and software configurations will continue to be supported
properly by the new release. If the information is not clear, contact
the Cisco Technical Assistance Center ("TAC") or your contracted
maintenance provider for assistance.
+--------------------------------------------+
| Affected Software | Fixed Software |
| Version | Version |
|----------------------+---------------------|
| Cisco IDS 4.1(5b) | Cisco IDS 4.1(5c) |
| and earlier | |
|----------------------+---------------------|
| Cisco IPS 5.0(6p1) | Cisco IPS 5.0(6p2) |
| and earlier | |
|----------------------+---------------------|
| Cisco IPS 5.1(1) and | Cisco IPS 5.1(2) |
| earlier | |
+--------------------------------------------+
Note: IPS version 5.1(2) is no longer available for download. It has
been replaced by IPS version 5.1(3).
Note: Bug ID CSCsd91720 is fixed in IPS version 5.0(6p1), and CSCsf12379
is fixed in IPS version 5.0(6p2).
Fixed software for Cisco IPS versions 5.1(x) are available for download
at http://www.cisco.com/pcgi-bin/tablebuild.pl/ips5?psrtdcat20e2
Fixed software for Cisco IPS versions 4.1(x) and 5.0(x) is available
for download at
http://www.cisco.com/pcgi-bin/tablebuild.pl/ids-patches?psrtdcat20e2
Workarounds
===========
It is possible to limit exposure to the web administration interface
SSL denial of service vulnerability by applying an access control list
(ACL) on an IPS/IDS device to restrict access to trusted management
systems. Instructions to add an ACL can be found at:
http://www.cisco.com/en/US/products/hw/vpndevc/ps4077/products_configuration_guide_chapter09186a008055df9a.html#wp1031536
There is no workaround for the fragmented packet IPS evasion
vulnerability.
Obtaining Fixed Software
========================
Cisco will make free software available to address this vulnerability
for affected customers. This advisory will be updated as fixed software
becomes available. Prior to deploying software, customers should
consult their maintenance provider or check the software for feature
set compatibility and known issues specific to their environment.
Customers may only install and expect support for the feature sets they
have purchased. By installing, downloading, accessing or otherwise
using such software upgrades, customers agree to be bound by the terms
of Cisco's software license terms found at
http://www.cisco.com/public/sw-license-agreement.html, or as otherwise
set forth at Cisco.com Downloads at
http://www.cisco.com/public/sw-center/sw-usingswc.shtml.
Do not contact either "psirt@cisco.com" or "security-alert@cisco.com"
for software upgrades.
Customers with Service Contracts
+-------------------------------
Customers with contracts should obtain upgraded software through their
regular update channels. For most customers, this means that upgrades
should be obtained through the Software Center on Cisco's worldwide
website at http://www.cisco.com.
Customers using Third Party Support Organizations
+------------------------------------------------
Customers whose Cisco products are provided or maintained through prior
or existing agreement with third-party support organizations such as
Cisco Partners, authorized resellers, or service providers should
contact that support organization for guidance and assistance with the
appropriate course of action in regards to this advisory.
The effectiveness of any workaround or fix is dependent on specific
customer situations such as product mix, network topology, traffic
behavior, and organizational mission. Due to the variety of affected
products and releases, customers should consult with their service
provider or support organization to ensure any applied workaround or
fix is the most appropriate for use in the intended network before it
is deployed.
Customers without Service Contracts
+----------------------------------
Customers who purchase direct from Cisco but who do not hold a Cisco
service contract and customers who purchase through third-party vendors
but are unsuccessful at obtaining fixed software through their point of
sale should get their upgrades by contacting the Cisco Technical
Assistance Center (TAC). TAC contacts are as follows.
* +1 800 553 2447 (toll free from within North America)
* +1 408 526 7209 (toll call from anywhere in the world)
* e-mail: tac@cisco.com
Have your product serial number available and give the URL of this
notice as evidence of your entitlement to a free upgrade. Free upgrades
for non-contract customers must be requested through the TAC.
Refer to http://www.cisco.com/warp/public/687/Directory/DirTAC.shtml
for additional TAC contact information, including special localized
telephone numbers and instructions and e-mail addresses for use in
various languages.
Exploitation and Public Announcements
=====================================
The Cisco PSIRT is not aware of any public announcements or malicious
use of the vulnerability described in this advisory.
The web administration interface SSL denial of service vulnerability
was discovered internally by Cisco.
The fragmented packet IPS evasion vulnerability was reported to Cisco
by Pratap Ramamurthy and Shai Rubin of the Wisconsin Safety Analyzer
group (WiSA) in the Computer Science department at the University of
Wisconsin.
Status of this Notice: FINAL
============================
THIS DOCUMENT IS PROVIDED ON AN "AS IS" BASIS AND DOES NOT IMPLY ANY
KIND OF GUARANTEE OR WARRANTY, INCLUDING THE WARRANTIES OF
MERCHANTABILITY OR FITNESS FOR A PARTICULAR USE. YOUR USE OF THE
INFORMATION ON THE DOCUMENT OR MATERIALS LINKED FROM THE DOCUMENT IS AT
YOUR OWN RISK. CISCO RESERVES THE RIGHT TO CHANGE OR UPDATE THIS
DOCUMENT AT ANY TIME.
A stand-alone copy or Paraphrase of the text of this document that
omits the distribution URL in the following section is an uncontrolled
copy, and may lack important information or contain factual errors.
Distribution
============
This advisory is posted on Cisco's worldwide website at:
http://www.cisco.com/warp/public/707/cisco-sa-20060920-ips.shtml
In addition to worldwide web posting, a text version of this notice is
clear-signed with the Cisco PSIRT PGP key and is posted to the
following e-mail and Usenet news recipients.
* cust-security-announce@cisco.com
* first-teams@first.org
* bugtraq@securityfocus.com
* vulnwatch@vulnwatch.org
* cisco@spot.colorado.edu
* cisco-nsp@puck.nether.net
* full-disclosure@lists.grok.org.uk
* comp.dcom.sys.cisco@newsgate.cisco.com
Future updates of this advisory, if any, will be placed on Cisco's
worldwide website, but may or may not be actively announced on mailing
lists or newsgroups. Users concerned about this problem are encouraged
to check the above URL for any updates.
Revision History
================
+----------------------------------------+
| Revision | | Initial |
| 1.0 | 2006-August-20 | public |
| | | release. |
+----------------------------------------+
Cisco Security Procedures
=========================
Complete information on reporting security vulnerabilities in Cisco
products, obtaining assistance with security incidents, and registering
to receive security information from Cisco, is available on Cisco's
worldwide website at
http://www.cisco.com/en/US/products/products_security_vulnerability_policy.html.
This includes instructions for press inquiries regarding Cisco security
notices. All Cisco security advisories are available at
http://www.cisco.com/go/psirt.
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All contents are Copyright 1992-2006 Cisco Systems, Inc. All rights
reserved.
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Updated: Sep 20, 2006 Document ID: 71558
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